40 



When the weather was favorable, the effect of gun fire and mines 

 was tried. Gunfire dislodged small sections of ice from the berg. 

 This method of attack is considered of inappreciable value. Very 

 little effect could be noted from mines fired alongside the berg at 

 depths of 4 or 5 fathoms. The mining showed also that a single mine 

 or even four had little or no more effect than to shake off loose ice and 

 possibly set up an internal strain. Mines planted under the berg or 

 shallow water near the side of berg, did more damage then those 

 fairly deep. The tamping effect of water at deeper depths was very 

 pronounced. 



Experiments to determine the effect of T. N. T. mines detonated 

 in the air on the surface of a berg were conducted and a large double- 

 ridged ''dry-dock" berg, approximately 500 feet long and 250 feet 

 high at the highest elevation, was chosen for the demonstration. 

 This berg which was guarded by the Modoc and Tampa during 

 the month of June, presented a smooth water polished shelf along 

 one side of its length 15 to 20 feet above level, which was scalable 

 with some difficulty, owing to the rounded edge on which the board- 

 ing party must leap from the boat. Steps were cut out on this 

 rounded face, and with the spiked shoes worn by the party, the 

 landing and disembarking were successfully accomplished without 

 accident. 



The shelf mined was about 40 feet in width, and terminated in a 

 cliff rising 150 feet above water from which dangerous falls of ice 

 might occur; but this cliff appeared to be stable, and the belief in 

 this regard proved correct, for no trouble was experienced from this 

 source. In fact, the whole berg at the time was in solid condition 

 and extremely resistant to the shock of the explosive; more favorable 

 conditions with a disintegrating berg would entail too much risk for 

 the mining party not commensurate with the results obtainable. 



Five successive charges were detonated in one spot, the first four 

 being the standard wTccking mine of about 65 pounds' charge of 

 T. N. T. and the last a pair of these mines of 130 pounds' charge. 

 The first mine laid on the surface of the shelf, about 20 feet back, 

 excavated a hole 3 feet deep and 10 feet across; when the last charge 

 had been set off the hole had increased in size to 15 feet deep and 

 20 feet across. On the rim of the hole a circular dyke of finely broken 

 ice had been deposited to a height of several feet. 



Very little effect was noticeable in falls of ice from the berg cliffs; 

 but it is thought strains may have been set up in the structure and 

 cracks started to account a day or two later for heavy falls when 

 water from the melting ice had found its way into these crevices and 

 accentuated them. 



Some doubt was felt regarding the effect of air pressures to be set 

 up by these mines detonated in air, inasmuch as there had been 

 no experience with them in that way. The shock was found to be 



